Water absorbent materials such as superabsorbent polymers can be employed in various applications, such as in disposable sanitary products (for example, diapers, incontinence articles, feminine hygiene products, airlaids and absorbent dressings), household articles, sealing materials, humectants for agricultural products for soil conditioning, oil-drilling, anti-condensation coatings, water-storing materials in agriculture/horticulture, absorbent paper products, bandages and surgical pads, pet litter, wound dressings, and as chemical absorbents. Furthermore, they can be employed in applications related to the transportation of fresh food or seafood, and in food packaging applications.
The largest use of superabsorbent materials, however, is in disposable personal hygiene products. These products include, in order of volume of superabsorbent material used, diapers, training pants, adult incontinence products and feminine hygiene products. Of these, diapers account for over 85% of the total amount of superabsorbent material sold in 2002 (Ohmura K., Nonwovens Industry, 2003, 34(5), p. 24). As a result, the development of superabsorbent materials has been largely focused on the creation of materials having optimal properties for absorbing urine.
The significant differences between the numerous fluids to be absorbed by the various disposable absorbent products, poses a substantial challenge to any manufacturer of hygiene products.
In the case of diapers, the fluid to be absorbed is typically urine, a fluid largely composed of water, salts and nitrogenous materials such as urea. In the case of feminine hygiene products, the fluid to be absorbed is typically menses, a complex fluid comprising water, mucous fluids, salts, proteins, fibrinogens, blood and cell debris (Björnberg, Nonwovens World, 2000, 9(2), pp 54-62). In such complex fluids, cells and clotted materials are too large to diffuse into the structural network of the superabsorbent material. Instead, they will adsorb onto the surface of the particles composing the superabsorbent material. Due to the high osmotic pressure of the partially swollen superabsorbent material, the cells and clotted materials will become dehydrated, leading to formation of a nearly impermeable layer surrounding the superabsorbent material. This essentially impermeable layer will seriously impede the efficacy of the superabsorbent material. The nature of the superabsorbent material used for absorbing complex fluids such as menses, should therefore be different from that used for absorbing simple fluids such as urine.
Various approaches have been disclosed regarding the development of superabsorbent materials capable of absorbing complex fluids such as menses. However, any improvement in the ability of these specifically designed superabsorbent materials to absorb complex fluids, was oftentimes offset by a diminishment in their ability to absorb simple fluids. Moreover, these specifically designed superabsorbent materials are often times more expensive in comparison to the mass-produced superabsorbent materials developed primarily for absorbing simple fluids such as urine.
The use of chemically treated superabsorbent materials having an enhanced ability to absorb complex fluids, has been previously described in a number of documents (Potts et al. U.S. Pat. No. 6,350,711; Di Luccion et al. WO 01/91684). While considered to be somewhat effective, these materials often involve complicated manufacturing processes, which invariably increase the cost of the resulting superabsorbent materials.
From the many approaches used to design superabsorbent materials capable of absorbing complex fluids, plant-based polymers, and clays or mineral compounds, have been found to be particularly useful.
There is a global demand for replacing petroleum-derived raw materials with renewable plant-based materials. The use of natural, biodegradable glass-like pregelatinized starches as absorbents for liquids has been disclosed by Le Groupe Lysac (Huppé et al. CA 2,308,537).
It was observed that modified starches could interact synergistically with mannose containing polysaccharides, ionic polysaccharides, gelling proteins or mixtures thereof (Bergeron, Calif. 2,426,478). These synergistic interactions have been found to be especially useful in formulating absorbent materials. The absorption characteristics of these modified starches could be attributed to amylopectin, a high molecular weight branched polymer of glucose. It was found that amylopectin, when crosslinked or networked, provides materials having improved absorbent properties (Le Groupe Lysac; Thibodeau et al. (CA 2,462,053)).
Le Groupe Lysac (Couture et al., CA 2,362,006) has previously disclosed polyethylene glycol crosslinked polysaccharides as being particularly useful absorbents. Other modified polysaccharides having improved absorbent properties have been previously reported by Qin et al. (U.S. Pat. No. 5,550,189; U.S. Pat. No. 5,498,705; and U.S. Pat. No. 5,470,964); Besemer et al. (WO 0035504A1; WO 0134656A1; and WO 9929352A1); Chung-Wai et al. (U.S. Pat. No. 5,932,017; U.S. Pat. No. 6,231,675; and U.S. Pat. No. 6,451,121); Shah et al. (U.S. Pat. No. 5,718,770); Shi et al. (U.S. Pat. No. 6,277,186); as well as by Beenackers A. A. C. M. et al. (Carbohydr. Polym., 2001, 45, 219-226).
The use of galactomanans, crosslinked with borate or zirconium ions, as absorbent polysaccharides, has been disclosed in a number of patents: U.S. Pat. No. 4,624,868; U.S. Pat. No. 4,333,461; JP 2002-253961; JP 2002-035037; JP 2001-278998; JP 2002-037924; JP 2002-053859; JP 2001-120992; JP 2002-053859; and JP 2001-226525. However, these polysaccharides suffer from syneresis and gel flowing problems.
Cottrell et al. (U.S. Pat. No. 5,536,825 and U.S. Pat. No. 5,489,674) disclosed the use of solvent (methanol or isopropanol) purified galactomanans as absorbent polysaccharides. Furthermore, Annergren et al. (WO 0021581A1) disclosed that soaking cross-linkable polysaccharides in methanol provides a material exhibiting superior absorbency. However, the use of alcohols imparts increased process costs in addition to requiring additional environmental precautions.
Even though the use of polysaccharide-based absorbent materials in personal care products is known, they have not gained wide acceptance in such applications. This is due, at least in part, to their absorbent properties being generally inferior to synthetic absorbent materials such as polyacrylates. Furthermore, many of the natural-based materials exhibit poor absorption properties, particularly when subjected to external pressures. Many of the natural-based materials tend to form soft, gelatinous masses, when swollen with a liquid. When employed in absorbent products, the presence of such soft gelatinous masses tends to prevent the passage of liquids (such as physiological solutions or aqueous solutions) through the fibrous matrix in which the absorbent material is incorporated. This phenomenon is known as gel blocking. Once gel blocking occurs, subsequent insults of liquid cannot be efficiently absorbed by the product, and the product tends to leak.
Clays, and other mineral compositions such as diatomaceous earth are environmentally friendly, naturally abundant and economic. Even though many types of clay are known for their liquid absorbing properties, their use is often restricted due to their colloidal, dispersive properties in water. The use of clays in combination with other ingredients such as polymers, has been previously disclosed.
Burkholder et al. (U.S. Pat. No. 3,935,363) disclosed that clay minerals having enhanced water-absorbing properties can be obtained when flocculated into granular aggregates using small amounts of an inorganic salt solution and/or a water-soluble polymeric flocculating agent such as polyacrylic acid, followed by drying.
Physical blends of clays and polyacrylates have also been reported by Shinji et al. (JP 10-244249), Kobayashi et al. (U.S. Pat. No. 5,489,469), McKinley et al. (U.S. Pat. No. 4,500,670), Richman et al. (U.S. Pat. No. 4,454,055), Sun et al. (U.S. Pat. No. 6,124,391), Roe et al. (U.S. Pat. No. 5,419,956), and Schöne (U.S. Pat. No. 6,175,055).
Physical blends of superabsorbents having clay aggregates on their surface to help them absorb physiological fluids have been disclosed by Herfert et al. (US2004018006 A1) and Reeves et al. (U.S. Pat. No. 6,387,495 and U.S. Pat. No. 6,376,011).
A blend of a bentonite clay (>85%) and a water swellable-water insoluble organic polymeric hydrocolloid, having improved absorbency for use in cat litter applications has been disclosed by Woodrum (U.S. Pat. No. 4,914,066). Cat litters comprising borax crosslinked galactomanans and bentonite have been disclosed by Marshall (US20040035369).
A dry blend of kieselguhr (diatomaceous earth) and organic gel formers (CMC, starch, dextrose, gelatin, etc.) for use in absorbent pads for food packaging has been disclosed by Marx (U.S. Pat. No. 4,615,923).
A dry blend including ionic polymers such as sodium carboxymethyl cellulose, ionic crosslinkers and clays has been disclosed by Brander (U.S. Pat. No. 6,376,034 and U.S. Pat. No. 5,820,955). These blends were disclosed as being particularly useful in food packaging applications as absorbent pads.
Polysaccharide-clay physical blends, even though offering synergistic performances with regards their absorption properties, do not possess the absorption capacities of modified polysaccharides or synthetic polymers.
Nanocomposites constitute a relatively new class of materials. As implied by the term “nanocomposites”, the constituents making-up the nanocomposite material are of nanometer size; one nanometer being one-millionth of a millimeter. Nanocomposite materials often exhibit properties, reflective of the materials making-up the composite. Nanocomposite materials can be synthesized using surprisingly simple and inexpensive techniques.
Clays are composed of phyllosilicates, also referred to as sheet-like silicates. These silicates have a thickness of about 1 nanometer (nm), while having a length and a width ranging from 300 to 500 nm. The size, composition and shape of phyllosilicates will vary depending on the clay source. Cations such as calcium, magnesium, sodium or potassium ions are located between phyllosilicates, in a “sandwich-type” arrangement. Upon exposure to an aqueous environment, these cations become hydrated, increasing the space between the distinct phyllosilicates, resulting in a swelling of the clay.
Phyllosilicate nanocomposites are materials comprising a nanoscale dispersion of phyllosilicates in a polymer network. Typical phyllosilicate nanocomposites are exfoliated nanocomposites, intercalated nanocomposites and semi-exfoliated nanocomposites.
Exfoliated nanocomposites are also referred to as “phyllosilicate dispersions”. Within these exfoliated nanocomposites, the phyllosilicates are delaminated and uniformly dispersed through the polymer network.
Intercalated nanocomposites are also referred to as “sandwich nanocomposites”. Intercalated nanocomposites are composed of repeating and alternating phyllosilicate-polymer layers.
Semi-exfoliated nanocomposites are composed of partially exfoliated clays. Within these semi-exfoliated nanocomposites, clays are delaminated into smaller units comprising from about 45 to 70 phyllosilicate blocks. Clays usually comprise units having from about 85 to 140 phyllosilicate blocks as defined by Chenu et al. (Comptes Rendus de I'Académie des Sciences, 1990, Série 2, 310 (7 série 2), PP. 975-980). These smaller phyllosilicate units are dispersed uniformly throughout the polymer network.
Nanocomposites can be prepared by numerous techniques. The most common technique involves ion exchange of the cations located in the interlayer spacing of the clays using cationic surfactants (cationic molecules bearing C8-C30 aliphatic chains). This technique was first reported by Okada et al. (Mat. Res. Soc. Proc., 1990, 171, 45-50) and subsequently by Pinnavaia et al. (U.S. Pat. No. 6,261,640; U.S. Pat. No. 6,414,069, and U.S. Pat. No. 6,261,640).
Techniques for increasing the interlayer spacing between the phyllosilicates making-up the clays have been disclosed by Beall et al. (U.S. Pat. No. 6,228,903 and U.S. Pat. No. 5,760,121); Lan et al. (U.S. Pat. No. 6,399,690); Qian et al. (U.S. Pat. No. 6,407,155); Zilg et al. (U.S. Pat. No. 6,197,849), Ross et al. (U.S. Pat. No. 6,521,690); Barbee et al. (US20020169246 A1); Ishida (U.S. Pat. No. 6,271,297); Powell et al. (U.S. Pat. No. 6,730,719); Knudson et al. (US20020165305 A1); Lorah et al. (US20030060555 A1); Fischer et al. (U.S. Pat. No. 6,579,927) and Bagrodia et al. (U.S. Pat. No. 6,586,500).
Nanocomposites have also been prepared using physico-chemical techniques such as extrusion, lyophilization, and ultrasonic wave treatments, as disclosed by Torkelson et al. (WO 2004043663); Lee et al. (US20030134942 A1); Nobuyoshi (JP 02-203936), and McClelland et al. (CA 2,352,502).
The use of organophilic clays such as activated quarternium-18 bentonite for the absorption and deactivation of fecal proteolytic enzymes, has been disclosed by Schulz (U.S. Pat. No. 5,869,033). These organophilic clays were used to prevent diaper rash.
Hybrid organic-inorganic gels for use in cosmetic or pharmaceutical compositions have been disclosed by Lahanas et al. (U.S. Pat. No. 6,042,839); Udagawa (JP 09-187493); Collin et al. (EP 1327435 A1); and Chevalier et al. (EP 1203789 A1). However, theses gels have not been reported as absorbent materials for use in hygiene related applications.
Starches have also been reported as being used as components in nanocomposite materials. Hydroxyapatite reinforced starch/ethylene-vinyl alcohol copolymer composites have been reported by Reis et al. (J. Adv. Polym. Technol. 1997, 16, 263). Calcined kaolin/thermoplastic starch composites have been disclosed by DeCarvalho et al. (Carbohydr. Polym. 2001, 45 (2), 189-194). Montmorillonite/thermoplastic starch hybrids have been described by Park et al. (Macromolecular Materials and Engineering, 2002, 287(8), pp. 553-558, J. of Mat. Sci, 2003, 38 (5), pp. 909-915) and McGlashan et al. (Polymer International, 2003, 52(11), PP 1767-1773). However, these starch containing nanocomposite materials were not reported as exhibiting absorbent properties.
The use of chitosan in nanocomposite materials has also been reported. Cationic chitosan, intercalated in montmorillonite, has been disclosed by Darder et al. (Chemistry of materials, 2003, 15 (20), PP 3774-3780). A butyl-acrylate-graft chitosan montmorillonite nanocomposite, has been reported by Li et al. (Radiation physics and chemistry, 2004, 69(6) APR, PP 467-471). The use of xanthan and scleroglucan in nanocomposite materials has also been reported.
Superabsorbent nanocomposites produced from ethylenically unsaturated monomers have been reported by Eiji et al. (JP 04-290547). Even though having a high absorption and retention capacity, they are made from non-renewable sources and are generally not biodegradable nor hypoallergenic. Polacrylamide nanocomposites have been reported by M'Bodj, O. et al. (Journal of Colloid and interface science, 2004, 273(2) (May 15), PP 675-684).
Starch-graft-polyacrylamide constitutes one of the superabsorbents with the highest water absorbency (Riccardo P. O., Water-Absorbent Polymers: A Patent Survey. J. Macromol. Sci., Rev. Macromol. Chem. Phys., 1994, 607-662 (p. 634) and references cited therein). However, due to high production costs and lower gel strength, starch-graft-polyacrylamide applications are limited.
The synthesis and properties of starch-graft-polyacrylamide/clay superabsorbent composites having enhanced absorbent properties, have been reported by Jihuai Wu et al. (Macromol. Rapid Commun. 2000, 21, (15), pp 1032-1034, Polymer, 2003, 44 (21), PP 6513-6520). However, these composite materials are neither biodegradable nor hypoallergenic.
Unfortunately, most modified polysaccharide-based materials do not possess absorptive properties comparable to many of the synthetic, highly absorptive materials, severely limiting their use as absorbent materials in personal hygiene products.
There thus remains a need for polysaccharide-clay highly absorbent nanocomposite materials suitable for use in personal hygiene products as well as methods for producing these highly absorbent nanocomposite materials.